Due to rapid increase of fossil fuel use, demand for use of alternative energy or clean energy is increasing, the field to be most actively studied as part of it is power generation and electricity storage using electrochemistry.
At present, a representative example of an electrochemical device using this electrochemical energy may include a rechargeable battery, and the usage area thereof is gradually expanding.
The rechargeable battery is classified into a cylindrical battery and an angular battery in which an electrode assembly is embedded in a cylindrical or angular metal can, and a pouch-shaped battery in which an electrode assembly is embedded in a pouch-shaped case of an aluminum laminate sheet, depending on the shape of a battery case.
The electrode assembly embedded in the battery case is a repeatedly chargeable and dischargeable power generation device composed of a stacked structure of positive electrode/separator/negative electrode, and classified into a jelly-roll type in which a separator is interposed between a negative electrode and a positive electrode in a long sheet shape having an active material coated thereon and wound, and a stack type in which a plurality of positive and negative electrodes having a predetermined size are sequentially stacked with a separator interposed therebetween.
As an electrode assembly having a more advanced structure of a mixed form of the jelly-roll type and the stack type, a stack/folding type electrode assembly in which a full cell having a positive electrode/separator/negative electrode structure or a bicell having a positive electrode (negative electrode)/separator/negative electrode (positive electrode)/separator/positive electrode (negative electrode) structure, having a constant unit size is folded using a long continuous separation film, has been developed.
In addition, in order to improve processability of the conventional stack type electrode assembly, and meet the demand of various types of rechargeable battery, a lamination/stack type electrode assembly having a structure formed by stacking unit cells in which electrodes and separators are stacked alternately and laminated has been also developed.
Meanwhile, an electrode which is a core constituent element of this rechargeable battery is manufactured by applying electrode slurry including an electrode active material, a binder, a solvent and the like on a current collector composed of metals, and performing drying.
During a drying process of the electrode slurry, binder particles are agglomerated around the surface of an electrode slurry layer. It is known that this phenomenon occurs, since vaporization of the solvent occurs on the surface of the electrode slurry layer during the drying process, and when the solvent in the inside moves to the vicinity of the surface by a capillary phenomenon, the binder which is solvated so that it is in a state of being flowable in the electrode slurry layer moves together to the vicinity of the surface of the electrode slurry layer.
When binder particles are agglomerated at the vicinity of the surface of the electrode slurry layer, as a whole of the electrode, dispersibility of the electrode active material and the like is deteriorated, and adhesion efficiency of the binder is lowered,
Eventually, binder particle agglomeration causes problems such as increased internal resistance of the electrode, deteriorated electrolyte solution impregnability, and overall performance degradation of the rechargeable battery.
Accordingly, there is a high need for technology to decrease binder agglomeration during the drying process of electrode slurry, thereby capable of improving dispersibility of an electrode active material, and increasing adhesion efficiency of a binder.